In an optical transmission system, degradation of a main signal occurs due to wavelength dispersion in optical fiber and the like, used as a transmission line. The worse a characteristic of the optical fiber, which is the transmission line, is, and the higher a bit rate of the main signal is, the larger this degradation becomes; for example, if a high bit rate signal of 10 Gbps or 40 Gbps is transmitted by an optical fiber with a poor characteristic, this degradation is significant, and feasible transmission distance becomes short.
Consequently, a method may be used in which a client signal is divided into N parts, and, with a bit rate of 1/N, is transmitted over a long distance by N optical wave paths. For example, Patent Document 1 discloses a configuration to reduce delay time when communicating in case of using this method.
Furthermore, Patent Document 2 also discloses a configuration in which transmittable distance of high-speed, large-volume tributary signals is extended, the tributary signals are demultiplexed for separation and are transmitted in the separated mode, and the signals that have been demultiplexed are multiplexed at a receiver side to restore the tributary signals.
Furthermore, Patent Document 3 discloses a configuration which, for a transceiver for wavelength multiplexing optical transmission, to which a plurality of terminal apparatuses are respectively connected, has a transponder in a standby system that switches when an abnormality is detected.
[Patent Document 1]
JP Patent Kokai Publication No. JP-P2003-51811A
[Patent Document 2]
JP Patent Kokai Publication No. JP-P2002-158638A
[Patent Document 3]
JP Patent Kokai Publication No. JP-A-10-210008